KSES: Allow SVG-specific presentation attributes in safe_style_css

[t-hamano]

See #78808 (comment)

What?

Adds a safe_style_css filter that allowlists SVG-specific presentation attributes so they are preserved when SVG markup is sanitized with wp_kses().

Why?

wp_kses() runs the style attribute through safecss_filter_attr(), which only keeps an allowlist of CSS properties. SVG presentation attributes are not in that list, so inline styles get stripped during sanitization.

This issue may become more prominent once stroke-based icons are implemented by #78808 or custom icons are allowed to be registered by #77260.

How?

Adds lib/compat/wordpress-7.1/kses.php with a single safe_style_css filter that appends the SVG presentation attributes. The list is based on the SVG presentation attributes documented on MDN.

Testing Instructions

add_action( 'admin_notices', function () {
	$svg = '<svg style="fill: none; stroke: red; stroke-width: 2;" viewbox="0 0 24 24">'
		. '<path style="fill-rule: evenodd; vector-effect: non-scaling-stroke;" d="M0 0h24"/></svg>';
	$allowed = array(
		'svg'  => array( 'style' => true, 'viewbox' => true ),
		'path' => array( 'style' => true, 'd' => true ),
	);
	echo '<div class="notice notice-info"><p><code>' . esc_html( wp_kses( $svg, $allowed ) ) . '</code></p></div>';
} );

Confirm that the styles are not removed when using the code above.

Use of AI Tools

This PR was authored with the assistance of Claude Code. All changes were reviewed by the author.

[github-actions]

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Co-authored-by: t-hamano <wildworks@git.wordpress.org>

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[github-actions]

Flaky tests detected in 9f9b1b3.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/27469026092
📝 Reported issues:

• [Flaky Test] should allow user to add and remove multiple local font files #78760 in /test/e2e/specs/admin/font-library.spec.js
• [Flaky Test] shouldn't conflict with server-side autosave #78706 in /test/e2e/specs/editor/various/autosave.spec.js